1. Field of the Invention
The present invention relates to a wavelength division multiplexed signal amplifying repeater for amplifying and relaying optical wavelength division multiplexed signals and an optical communication transmission line using such repeaters.
2. Description of the Background Art
An optical fiber transmission line using optical amplifiers has a good affinity with the optical wavelength division multiplexed communications as the optical amplifiers can amplify optical wavelength division multiplexed signals collectively, and there has been a report of a long distance transmission experiment for over 9000 km.
However, the erbium doped optical fiber amplifier (abbreviated hereafter as EDFA) that is the optical amplifier used in the 1.55 xcexcm band that is the wavelength band for the long distance optical communications has the amplification bandwidth of about 40 nm from 1530 nm to 1570 nm, so that the upper bound of the number of wavelengths that can be wavelength division multiplexed is about 50 wavelengths for the wavelength division multiplexed signals with a wavelength separation of 100 GHz that are standardized by the ITU-T (International Telecommunications Union-Telecommunication sector).
Recently, there has been a report of a gain shifted EDFA in which the gain bandwidth of EDFA is shifted toward the long wavelength side. This gain shifted EDFA has the amplification bandwidth of about 40 nm from 1580 nm to 1620 nm, and there has also been a report of an optical amplifier in which the gain bandwidth is almost doubled by combining this gain shifted EDFA with the usual EDFA. However, even in such a case, the upper bound of the number of wavelengths that can be wavelength division multiplexed is about 100 wavelengths.
The transmission capacity required in the future optical fiber communications is expected to be a very large capacity of several Tbit/s. At a research level, there has already been a report of a transmission of as many wavelength division multiplexed signals as 2.6 Tbit/s in total (Y. Yano, et al., xe2x80x9c2.6 Terabit/s WDM transmission experiment using optical duobinary codingxe2x80x9d, ECOC""96, Paper ThB.3.3, 1996).
In order to realize such a transmission capacity using SDH (Synchronous Digital Hierarchy) standard bit rate of STM-64 (10 Gbit/s) as a capacity per one wavelength, it is expected that the number of wavelengths that can be wavelength division multiplexed at a level of 100 wavelengths is insufficient and at least 200 wavelengths or more will be necessary.
As described above, there has been no technique for constructing an optical communication transmission line with a very large capacity of several Tbit/s in accordance with the international standards such as ITU-T standard and SDH standard.
It is therefore an object of the present invention to provide an optical wavelength division multiplexed signal amplifying repeater capable of doubling the number of wavelength division multiplexed signals that can be transmitted so that it becomes possible to realize an optical communication transmission line with a very large capacity of several Tbit/s.
It is another object of the present invention to provide an optical communication transmission line using such repeaters.
According to one aspect of the present invention there is provided an optical wavelength division multiplexed signal amplifying repeater, comprising: an optical amplification unit for amplifying optical signals of both 1.3 xcexcm band and 1.55 xcexcm band in optical wavelength division multiplexed signals entered from an input optical fiber; a pumping light source for providing pumping lights capable of causing Raman amplification in the 1.3 xcexcm band; and an optical coupling unit for coupling the pumping lights from the pumping light source with the optical wavelength division multiplexed signals so as to cause the Raman amplification for the optical signals of the 1.3 xcexcm band, such that the optical wavelength division multiplexed signals in which the optical signals of the 1.3 xcexcm band and the 1.55 xcexcm band are amplified by the optical amplification unit and the Raman amplification is caused for the optical signals of the 1.3 xcexcm band by the pumping lights that are coupled with the wavelength division multiplexed signals by the optical coupling unit are outputted to an output optical fiber.
According to another aspect of the present invention there is provided an optical communication transmission line, comprising: a plurality of optical wavelength division multiplexed signal amplifying repeaters, each having: an optical amplification unit for amplifying optical signals of both 1.3 xcexcm band and 1.55 xcexcm band in optical wavelength division multiplexed signals entered from an input optical fiber; a pumping light source for providing pumping lights capable of causing Raman amplification in the 1.3 xcexcm band; and an optical coupling unit for coupling the pumping lights from the pumping light source with the optical wavelength division multiplexed signals so as to cause the Raman amplification for the optical signals of the 1.3 xcexcm band, such that the optical wavelength division multiplexed signals in which the optical signals of the 1.3 xcexcm band and the 1.55 xcexcm band are amplified by the optical amplification unit and the Raman amplification is caused for the optical signals of the 1.3 xcexcm band by the pumping lights that are coupled with the wavelength division multiplexed signals by the optical coupling unit are outputted to an output optical fiber; and optical fibers connecting the optical wavelength division multiplexed signal amplifying repeaters in series.
Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.